Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations present, the description carries the burden well: it discloses the data source (DMI), the cost and payment mechanism (0.005 USD per call via x402), the measurement datum (cm relative to DVR90), and that the data is 'latest'/real-time. It does not cover failure modes, e.g. what happens when a port name matches multiple stations or no station.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences: what it returns, when it's useful, then provenance/price. The returned quantities and units are front-loaded and nothing is redundant.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Absent an output schema, the description must convey return contents, and it does: sea level in cm relative to DVR90 plus water temperature, from DMI. It omits the temperature unit and whether other fields (e.g. station metadata, timestamp) come back, which leaves a small gap for a single-parameter data lookup.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% (baseline 3), and the description adds real value on top by supplying concrete port-name examples that clarify what a valid value looks like. Partial-match behavior is documented in the schema rather than the description, so no further credit is warranted.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific resource and verb: 'Latest sea level ... and water temperature at Danish ports/tide gauges by port name', with concrete examples (Esbjerg, Aarhus, Skagen). An agent can immediately distinguish this from the generic dk_weather sibling and knows exactly what it retrieves.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives explicit usage contexts — port calls, draught and storm surge checks — which tells the agent when this is the right tool. It doesn't name an alternative (e.g. dk_weather) or state when not to use it, so it stops short of full routing guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.